Lice thrived before dinosaur extinction

06 April 2011

44-million-year-old fossil louse (species Megamenopon rasnitsyni) from Eckfeld Maar crater, Germany, on the left, is possibly the only known fossil bird louse. On the right is a close relative (species Holomenopon brevithoracicum) that lives on waterfowl.

The ancestors of today’s lice, and their bird and mammal hosts, were thriving and diversifying into different species before, not after, dinosaurs went extinct. So say scientists in a report in today's journal Biology Letters.

An international team, including scientists at the Natural History Museum, carried out a genetic and fossil study and produced a family tree showing the evolutionary history of lice. By putting a time-scale on this family tree, their data suggests that dinosaurs probably had lice.

Parasitic lice are dependent on their hosts such as birds and mammals for their survival. This dependency is so strong that their evolutionary histories are closely tied together. Many lice have evolved body shapes that allow them to live on specific parts of the host body. For example, wing lice are often adapted to the space between the barbs of wing feathers. The different sizes of this gap in different bird species makes it hard for the lice to ever change hosts.

Close-up of ostrich louse species, Struthiolipeurus. This study found that lice were diversifying, along with their bird and mammal hosts, before the dinosaurs went extinct 65 million years ago.

The team showed that parasitic lice evolved about 130 million years ago and that they were already diversifying before the event that caused the extinction of the dinosaurs and many other animals 65 million years ago.

If lice were diversifying, so too were their bird and mammal hosts, the team says. ‘Lice are like living fossils,’ says Cybertaxonomist Dr Vince Smith at the Natural History Museum who led the research. ‘The record of our past is written in these parasites, and by reconstructing their evolutionary history we can use lice as markers to investigate the evolutionary history of their hosts.’

This research supports the idea that some of the major groups of birds and mammals around today were present before the dinosaurs went extinct, rather than the other main theory that they diversified after the dinosaurs had died out.

Genetic and fossil studies

Close-up of mammal louse Trichophilopterus babakotophilus from a Madagascan lemur.

The team compared the DNA sequences of genes from 69 living louse species. Changes in the genes are a reliable measure of relatedness among different species in the same group. These changes accumulate over time and can be used to work out a rough timeline of the evolution of related groups of organisms.

Their study also included louse fossils that are extremely well preserved: a 44-million-year-old bird louse fossil and a 100 million-year-old book louse fossil (family Liposcedididae), which is a close relative of modern parasitic lice.

Did dinosaurs have lice?

The results revealed that lice were around at a time when feathered dinosaurs lived. Feathers, along with hair and fur on mammals, are a habitat and food resource for lice.

Kevin Johnson of the University of Illinois who was part of the research team adds, ‘Our analysis suggests that both bird and mammal lice began to diversify before the mass extinction of dinosaurs.

'And given how widespread lice are on birds, in particular, and also to some extent on mammals, they probably existed on a wide variety of hosts in the past, possibly including dinosaurs.’